1. Field of the Invention
The present invention relates to emulsifying agents for emulsion polymerization. More specifically, it relates to emulsifying agents suitable for use in the emulsion polymerization of polymer emulsions capable of forming a film having an excellent water resistance, transparency, and smoothness.
2. Description of the Related Art
Various surfactants have been heretofore used as emulsifying agents in the production of polymer emulsions from the emulsion polymerization of unsaturated monomers. Of these surfactants, cationic surfactants such as alkyl trimethyl ammonium salts, dialkyl dimethyl ammonium salts, polyoxyethylene alkyl amine, polyoxyethylene alkyl trimethylene diamine, polyoxyethylene alkylmethyl ammonium salts, polyoxyethylene alkyl dimethyl trimethylene ammonium salts, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolium betaine, 2-alkyl-N-carboxyethyl-N-hydroxyethyl imidazolium betaine, and N-alkyl dimethyl amine oxide are widely used.
When the above-mentioned conventional emulsifying agents are used, however, a large amount of agglomerates are formed during the polymerization and the particle sizes of the resultant polymer emulsions become large. In addition, the mechanical stability, chemical stability, and storage stability of the resultant polymer emulsions are adversely affected due to the use of the conventional emulsifying agents. Furthermore, when the polymer emulsions are used as a coating composition and an adhesive, the properties thereof are also affected due to the use of the conventional emulsifying agents.
On the other hand, it has been proposed in, for example, Angew. Chem. ,71, 604 (1959) that decomposable glycine betaine alkyl esters be used as a cationic surfactant to solve the above-mentioned problems. However, when the glycine betaine alkyl esters are used as an emulsifying agent, the film formed from the resultant polymer emulsion has a poor water resistance, transparency, and smoothness.